Dental caries is a common disease process that afflicts a large proportion of the world population. Extensive research indicates that dental caries is the result of a bacterial infection (Loesche, W. J., Microbiol. Rev. 50:353-380, 1986), but is also influenced by host and dietary factors (Hicks, J., et al., J. Clin. Pediatr. Dent. 28:47-52, 2003). Current research seeks to identify risk factors for caries, and to identify natural oral defenses that may protect against, or prevent, caries development. Salivary defense systems play a significant role in maintaining the health of the oral cavity and preventing caries. These defenses include factors which inhibit or reverse demineralization of exposed tooth surfaces, such as simple mechanical rinsing, buffering action, and calcium phosphate binding proteins, as well as antimicrobial activities including microorganism aggregation and clearance from the oral cavity, immune surveillance, and the secretion of antimicrobial peptides (Van Nieuw Amerongen, A., et al., Caries Res. 38:247-253, 2004).
Antimicrobial peptides (AMPs) are natural antibiotics that provide a first line of defense against a wide spectrum of pathogens (Ganz, T., Nat. Rev. Immunol. 3:710-720, 2003; Yang, D., et al., Annual Rev. Immunol. 22:181-215, 2004; Zasloff, M., Nature 415:389-395, 2002). The three main AMP families are defined by amino acid composition and three-dimensional structure: α-helical peptides without cysteine (the cathelicidins) (Bals, R., et al., Cell Mol. Life Sci. 60:711-720, 2003); peptides with three disulphide bonds (the α- and β-defensins) (Ganz, T., Nat. Rev. Immunol. 3:710-720, 2003; Ganz, T., et al., J. Clin. Invest. 76:1427-1435, 1985); and peptides with an unusually high proportion of specific amino acids, for example, the histatins (Oppenheim, F. G., et al., J. Biol. Chem. 263:7472-7477, 1988).
The human β-defensins (hBDs) are widely expressed in oral tissues and in gingival epithelium (Dale, B. A., et al., J. Periodontal Res. 36:285-294, 2001; Dunsche, A., et al., Eur. J. Oral Sci. 110:121-124, 2002; Zhao, C., et al., FEBS Letters 396:319-322, 1996). HBD1 and 2 have also been detected in salivary glands and ducts and in saliva (Bonass, W. A., et al., Oral Microbiol. Immunol. 14:371-374, 1999; Sahasrabudhe, K. S., et al., J. Dental Res. 79:1669-1674, 2000). The α-defensins, HNP 1, HNP 2, and HNP 3, are expressed in neutrophils, and participate in non-oxidative microbial death (Ganz, T., et al., J. Clin. Invest. 76:1427-1435, 1985), and have been identified in gingival crevicular fluid (McKay, M. S., et al., Oral Microbiol. Immunol. 14:190-193, 1999). The human cathelicidin peptide, LL37, is found in neutrophils and inflamed epithelia as well as in saliva (Murakami, M., et al., J. Dental Res. 81:845-850, 2002). Both the mRNA and protein for cathelicidin peptides have been localized to the salivary glands, specifically in acinar cells of the submandibular gland and palatine minor glands, as well as in lingual epithelium and palatal mucosa in mice (Murakami, M., et al., J. Dental Res. 81:845-850, 2002) and submandibular duct cells in humans (Woo, J. S., et al., Arch. Otolaryngol Head Neck Surg. 129:211-214, 2003).
The defensins and cathelicidins have broad antimicrobial activity against Gram-negative and Gram-positive bacteria and Candida albicans, and are effective, in vitro, against oral microorganisms such as Streptococcus mutans, Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans (Dale, B. A., et al., in R. L. Gallo (ed.), Horizon Bioscience, pp. 223-251, Wymondham, 2004; Joly, S., et al., J. Clin. Microbiol. 42:1024-1029, 2004; Nishimura, E., et al., Curr. Microbiol. 48:85-87, 2004; Tanaka, D., et al., Oral Microbiol. Immunol. 15:226-231, 2000). The cathelicidins and α- and β-defensins act synergistically with other antimicrobials (Maisetta, G., et al., Antimicrob. Agents Chemother. 47:3349-3351, 2003; Nagaoka, I., et al., Inflamm. Res. 49:73-79, 2000).
Despite improved knowledge of the various antimicrobial agents present in human saliva, there remains a need for methods to identify human beings who are susceptible to dental caries, and who will likely benefit from prophylactic measures to prevent tooth decay.